Transmittable Degenerative Encephalopathies (TDE) include bovine spongiform encephalopathy (BSE or “mad cow disease”), scrapie in sheep, Creutzfeldt-Jacob Disease (CJD), Gerstman-Straussler Schemker (GSS) and Kuru in humans. These diseases have achieved considerable notoriety in recent years at least partly due to the perception that authorities failed to monitor incorporation of BSE-contaminated beef into human and animal food supplies, which led to outbreaks of CJD, mainly in the United Kingdom (see Editorial in Nature, 1997, 389 423).
It is now well established that the agent responsible for TDE transmission is a protein, generally referred to as a “prion” protein, which underlies both BSE and CJD (Hill et al., Nature 1997, 389 448).
Generally, it has been concluded that the destruction of TDE in meat requires treatment at 132° C. for 20 minutes under 3 bars pressure. Alternatively, in the presence of alkali the temperature and pressure may be reduced to 121° C. and 2 bars respectively.
Alkali is known for its hydrolytic effect upon biomolecules such as proteins, and efforts to sterilize animal tissue contaminated with TDE have utilized alkali treatment, heat and pressure as means for destroying prion pathogenicity.
For example, Taguchi et al., 1991, Arch. Virol. 119 297 used a 1 hour treatment with 1 N NaOH followed by autoclaving at 121° C. for 30 minutes to inactivate CJD-infected brain homogenates. Ernst & Race, 1993, J. Virol. Methods 41 193 employed autoclaving together with NaOH and LpH treatment inactivate scrapie-infected brain homogenates.
A more extensive series of tests was performed by Taylor et al., 1994, Arch. Virol. 139 131 to decontaminate BSE-infected bovine brain or scrapie-infected rodent brain samples. Treatments included 1 M or 2 M NaOH for up to 1 hour, autoclaving at temperatures between 134° C. and 138° C. for up to 1 hour or treatment with sodium hypochlorite or sodium dichloroisocyanurate for up to 2 hours. These authors concluded that none of the procedures tested produced complete TDE inactivation.
The problem for manufacture of animal feed from potentially TDE-infected animal tissue is that high temperature and pressure conditions are not readily achievable using standard rendering or animal waste recycling equipment. Also, high temperature treatments during manufacture of animal feed tend to produce an inferior feed having unwanted by-products such as carcinogens, di-amino acids and volatile odors.